Princeton University is under federal investigation for discrimination after a conservative activist said he filed a complaint about a pro-Palestinian protest on campus. The investigation began April 4, according to a list of schools under investigation updated Wednesday by the U.S. Department of Education’s Office for Civil Rights. Princeton University joins Rutgers University and the public school districts in Newark, Teaneck and South Orange-Maplewood on the list. All are under investigation for alleged discrimination based on shared ancestry, which can mean antisemitism or other bias based…